1. Sand dollars are sea urchins
It’s true – sand dollars are a type of sea urchin. Rather than having long pointy spines, sand dollars have short, fuzzy spines on the outside of their shells.
2. Living sand dollars are covered in hairs that are covered in hairs.
The sand dollars’ hairs are also covered in smaller hairs called cilia. These all help the sand dollar move and eat.
3. Sand dollars burrow
Sand dollars often burrow to hide (from predators or strong currents) or eat. Otherwise, sand dollars often stand on edge.
4. The sand dollars you find on the shore are skeletons
The sand dollars found on shore are smooth, hard and usually bleached white by the sun. In life, the outside of a sand dollar would be soft and could be a variety of colors.
5. Sand dollars have silly common names
The name “sand dollar” is a common name for the sea urchins of the order Clypeasteroida.
However, that isn’t the only name they are called. Other names include sand cake, cake urchin, pansy shell and sea biscuit.
6. Sand dollars breathe through their spines
This comes from being buried most of the time. The spines on sand dollars’ back double as the animal’s gills.
7. In rougher waters, young sand dollars swallow sand
Rough waters are bad for sand dollars, who have no strong way to stop themselves from being washed around through the water. Adults are heavy enough that they simply lie flat and cling to the floor, but young animals are forced to swallow sand to give themselves added weight.
8. Sand dollars crowd together
Like many other ocean creatures, sand dollars crowd together on the ocean floor. Sand dollars congregate in groups of up to 625 in areas with very fine or muddy bottoms (this is the sand dollar’s best living environment).
9. You can tell the age of a sand dollar like a tree
Scientists age a sand dollar specimen by simply counting the rings in the sand dollars’ exoskeleton (they don’t have to count high – sand dollars usually live between six and 10 years).
10. Sand dollars are slow eaters
Sand dollars only have five teeth (sort of – they are only tooth-like, not real teeth), and chew their food for a long time – sometimes up to 15 minutes before swallowing. It can take the sand dollar up to two days to digest its food.
11. Sand dollars reproduce free-form
When sand dollars reproduce, their rigid exoskeleton restricts their mating and baby-creation methods. So, sand dollars figured, why not cut out the middleman and just let the babies make themselves? Sand dollars reproduce by spraying both sperm and egg into the open water and letting the larvae come together on their own.